Apparatus for and method of dimpling work sheets



March 20, 1956 c. J. SWAIN ETAL 2,738,575

APPARATUS FOR AND METHOD OF DIMPLING WORK SHEETS Filed Nov. 10, 1952 FIG. I.

INVENTORS CHARLES J. SWAIN ROY V. YOUNG JR.

mm M

ATTORNEYS APPARATUS non AND METHOD on DIMPLING WORK SHEETS United States Patent Charles J. Swain, Santa Monica, and Roy V. Young, Jr.,

Los Angeles, Calif., assignors to Zephyr Manufacturing Company, Manufacturing Division, a corporation of California Application November 10, 1952, Serial No. 319,761

Claims. (01'. 29-545) This invention has to do with methods of and apparatus for forming dimples about rivet and screw holes in sheet metal or the like.

As is well known, it is necessary to countersink the heads of rivets or screws used to secure work sheets together or to structural members, particularly in aircraft and similar construction work. However, in known meth- 2,738,575 Patented Mar. 20, 1956 die assembly or member and 6 the punch assembly or member which I employ in carrying out my invention.

The ram assembly or member comprises a hydraulically actuated reciprocal die body carried by a hydraulically actuated plunger 14. The die body has a frusto-conical cavity 17 in its lower end bounded by an annular fiat sheet engaging surface 19, and has a longitudinal bore 16 which presents an upwardly facing annular shoulder 20. A hydraulically actuated ram is mounted in the die body for axial movement relative thereto, the lower end of the ram abutting a ram button 26. The ram button has a relatively large diameter inner end portion 27 intersecting a smaller diameter outer end portion 28 in a conical shoulder 29 engageable with shoulder 20. The outer end of the ram button has a pilot pin receiving recess 30. The pressure loading ram 25 is relatively less "ice . than that loading plunger 14.

ods of and apparatus for forming such dimples in work sheets, a long existing difiiculty has been the resultant sheet warpage. That is, during the forming and coining of the dimple in the sheet there is a flow of the metal both inwardly towards the apex of the dimple as well as outwardly towards the base of the dimple, and this latter metal. tends to work out into the surrounding portion of the sheet-and cause warpage. It has been proposed, for instance, to overcome this flow of metal into that portion of theish eet surrounding the dimple by clamping the sheet between the punch and die members aroundthe area to be occupied by the dimple before the folding and coining of the dimple is commenced, but this procedure has the difi'lculty that a shearing stress is set up at the intersection of the dimple and surrounding sheet portion. 7

It is, therefore, among the principal aims and objects of my invention to provide apparatus for and method of performing the dimpling operation in such amanner as will substantially eliminate the dangers of warpage of the work sheet, as well as the dangers of weakening the sheet.

Itis also an object to provide, in such apparatus, novel means for stripping the dimple from the forming element after the dimple is formed.

Other objects and advantages will appear hereinafter.

Without intending thereby to limit the broader scope of the invention, except as may appear from the abandoned claims, I shall now describe a presently preferred apparatus and procedure for carrying out my invention, for which purpose I shall refer to the accompanying drawings wherein:

Fig. 1 is a medial, longitudinal section of the punch and die assemblies in the positions which they occupy at the start of a dimpling operation;

Fig. 2 is a section taken in line 2-2 of Fig. 1;

Figs. 3, 4 and 5 are sectional views of the ram and punch assemblies showing consecutive positions during a dimpling operation; and

Fig. 6 is a sectional view of punch elements after completion of a dimpling operation, and showing the dimple about to be stripped from the punch.

In general I have found that I am able substantially to overcome the danger of sheet warpage resulting from the dimpling operation by accomplishing the folding? or initial shaping of the dimple before applying clamping action to the work sheet, and then clamping the sheet around the folded or initially formed dimple after the folding is substantially completed and the coining operation commenced.

In the drawing, the numeral 5 generally denotes the The punch assembly includes a base 40 having an axial bore 41, three longitudinal passageways 42 radially ofiset from and equidistantly spaced apart around the bore 41, and an enlarged recess 43 at its lower end to threadedly receive a support 44.

A punch element 50 has a reduced cylindrical upper portion 51 providing an upwardly facing annular shoulder 52, portion 51 presenting a frusto-conical surface 53 conforming to recess of the ram button, and terminates in a pilot portion 54 which is of a diameter to fit the rivet hole S in the work sheet S. An annular punch pad 66 is supported upon three equidistantly circumferentially spaced pins 61 mounted in recesses 42, which pins in turn are supported upon the headed end 63a of a plunger 63 which is pressure-loaded at its lower end, as by a pressure-controlled pneumatic diaphragm (not shown). The plunger 63 is shown in a raised position, being movable downwardly within the body 44 in the course of operation as hereinafter explained.

It will be understood, of course, that while I have described the die assembly as being movable towards a relatively stationary punch, which arrangement I find to be preferable, it is within the purview of my invention to reverse this order, or to make both said elements movable relatively to each other. In either event, however, the punch pad 60 is yieldable to a limited extent relative to the punch.

In carrying out my method the work sheet S, in which the rivet or screw hole S has previously been bored or punched, is placed on the punch with the pilot 54 inserted in the hole as shown in Fig. 1.

Next, as shown in Fig. 3, the die assembly is moved downwardly, first bringing the annular fiat surface 19 of the die body into contact with the work sheet around the area to be occupied-by the dimple. In this position the the dimple D is substantialy folded between the surfaces 17 and 53, although, up to this stage, no coining pressure has been exerted upon the sheet. Due to the difierential of pressure on the die body through plunger 14 and that imposed upon the ram 25, the ram button recedes to the position of Fig. 4.

Further downward movement of the die assembly causes the sheet to be resiliently'clampedaround the dimple between die surface 19 and the surface 62 of the punch pad-the extent of the clamping pressure being determined by the pressure difierential as between that imposed upon plunger 14 to move the die downwardly and that imposed upon plunger 63 to resist yielding of the punch pad 60, the former pressure being relatively greater than the latter. Thus, during the movement from the position of Fig. 4 to that of Fig. 5, the final shaping of the dimple is ett'ected and the coining pressureis applied to the dimple while the sheet area immediately around the dimple is firmly but resiliently clamped. This coining results in a slight thinning of the dimple. When the parts reach the position of Fig. 5, the limit of yieldability of the punch pad is reached, that is the bottom of punch pad 60 and its inwardly flared portion 60:: will have abutted the top of the base 40 and the annular shoulder 52, respectively, in which position the surface 62 is coplanar with the base of surface 53. At the moment this limit is reached, the dimple becomes set to substantially compensate for the tendency of the dimple to spring back when the coining pressure is released.

After the forming and coining operations have thus been completed, the die assembly is raised to its initial position (Fig. l) and as this movement takes place the pneumatic pressure upon the punch pad raises the latter to its initial position "thus stripping the dimple from the punch core as shown in Fig. 5.

I claim:

1. The method of forming a coined dimple in a metallic work sheet in a manner substantially to prevent flow of material of the sheet from the dimpled area into the surrounding area, comprising the sequential steps of first preliminarily bending a portion of said sheet into the form of a conical dimple without applying coining pressure thereto and without applying clamping pressure to the surrounding portion of *said sheet, then applying coining pressure to said dimpled p'ortion While resiliently clamping said surrounding portion between fiat parallel surfaces, and then non-yieldably clamping said surrounding portion between said surfaces while continuing application of said coining pressure to said dimpled portion.

2. In sheet dir'nplin'g apparatus, the combination of a first forming member having a central conical forming portion and a surrounding, annular, fiat sheet clamping portion, a second forming member comprising a stationarily supported body having an axial opening, a forming element having an inner end portion secured in said opening and having a conical outer end portion arranged to mate with said central conical forming portion of said first forming member, an annular pad surrounding said forming element and presenting an annular fiat surface parallel to and facing said fiat sheet clamping portion of said first forming member, said body having a plurality of circumferentially spaced axial holes arranged around saidopening and extending through said body, pins axially slidably mounted in said respective holes and engaging said pad at their outer ends, and controlled pressure actuated means yieldably opposing axial movement of said pins inwardly of said body; said forming members being mounted for relative axial movement.

3. -In apparatus for forming, in conjunction with a die, a dimple in a metallic work sheet, a punch member comprising a body, a punch element secured in said body and having a conical outer end portion, a plurality of pins axially slidably mounted in said body, a yieldable pressure loaded plunger bearing against the inner ends of said pins, an annular punch pad surrounding said punch element and normally resting at its inner end upon the outer ends of said pins, said punch pad having a flat annular outer end surface and being axially movable relative to said punch element, and stop means arranged to limit axial movement of said punch pad relative to punch element.

'4 In apparatus for forming and coining a dimple in a perforated metallic w'ork sheet, a die member comprising a body having an axial bore, a frusto-conical cavity in its outer end, an annular flat surface surrounding said cavity, and a pressure loaded the button slidably "mounted in said bore and normally extending at its outer end into said cavity, said die button having an axial recess in its outer end; a punch member comprising a body, a punch element secured in said body and having a frusto-conical Outer end portion terminating in a pilot element insertable through a perforation in said sheet and engageable in said recess in said die button, a plurality of pins slidably mounted in said latter body, a yieldable pressure loaded plunger bearing against the inner ends of said pins, an annular punch pad surrounding said punch element and normally resting at its inner end upon the outer ends of said pins, said punch pad having a fiat, annular outer end surface opposed to and registering with said flat annular surface of the die member and being axially movable relative to said punch element, stop means arranged to limit axial movement of said punch pad relative to said 'punch element; and pressure actuated means for moving one of said bodies towards the other with relatively greater force than that at which said pressure loaded plunger yields; said 'fruSto-conical outer end portions of said punch element normally projecting from said punch pad towards said die member. 1

5. In a sheet dimpling apparatus, the combination of a first forming member comprising a die body having an axial bore flaring at its outer end into frust'o-con'ie'al shape, said bore having a restricted diameter portion adjacent its said outer end, a ram button axially slidably disposed in said bore and normally positioned so thatits outer end portion terminates flush with the outer end of said die body, said ram button having an axial recess in its outer end, a hydraulically actuated rain reciproeably mounted in said body and hearing at its outer end against said ram button to yieldably urge said ram button into said normal position, said die body having an annular flat surface surrounding said portion of frusto coni'cal shape, a second forming member comprising a rigidly supported body having an axial opening, a forming element having its inner end portion secured in said "opening and having a frustoconical outer end portion terminating in a pilot pin portion engageable in said recess in said ram button, an annular pad surrounding said forming element and presenting an annular, flat outer end surface parallel to and facing said first named fiat surface, said rigidly supported body having a plurality of circumferentially spaced holes extending axially therethroug'h, pins axially slidably mounted in said respective holes and engaging said pad at their outer ends, and controlled pressure actua'ted means yieldably opposing axial movement or said pins inwardly of said rigidly supported body; said pins and said pressure actuated means yieldably retaining *said pad in position with its said annular flat surface disposed in a plane bise'cting 'said frus'to-conical outer end portion of said forming element at a point spaced between base and apex portions, and one of said forming members being axially movable relative to the other.

References Cited in the file of this patent UNITED STATES PATENTS Re.23,939 Keller Feb. 8, 1-9-55 2,438,837 Archer Mar. 39, 1948 ZAf lJQQ B n M y 18, 948 2,483,799 Veit 0cc4, 1949 2,491,717 Creighton Dec. 20, I949 FOREIGN PATENTS 511,106 Great Britain Aug. 14, 1-939 

